Capillary and cleft electrospinners: (a) capillary electrospinner consists of a needle∕capillary (1) that is connected to a container (2), filled with polymer solution, through a flexible tube. A high voltage source (3) generates electrostatic field in the region between the needle and a collector (4). Whipping jet (5) transports the polymer solution from the needle to the disk collector on which nanofibers are collected in layers. The difference in the liquid levels of the container and the needle rim provides a hydrostatic pressure. (b) In a cleft electrospinner, the needle is replaced by two metallic plates (6) of length , height , and a cleft of breadth between them. The outer width of the cleft is . Upper edges of both the plates are serrated as shown in the magnified upright part (6). Several polymeric jets (7) are created on a free liquid surface when sufficient field strength is applied.
Relationship between the square of the angular frequency and the wave number for distilled water: curves 1, 2, and 3 represent relationships between the square of the angular frequency and the wave number , for field strength values, , , and , respectively. Critical wave number is as is evident from curve No. 1. The values of water surface tension , water density , gravity acceleration , and electric permittivity used for the plot are , , , .
Dependence of the wavelength on the critical field strength, . The relationship, according to Eq. (9) is plotted for distilled water with permittivity . Critical field strengths, according to Zeleny’s observations (Ref. 8) are plotted for capillary radii up to with empty circles. They have a standard deviation of about 2%. For greater capillary radii, Zeleny’s extrapolation, according to the formula , is used to plot the point with bold circles. The comparison is based on the relationship . All experimental data are plotted for distilled water with surface tension of , negligibly small hydrostatic pressure and ambient temperature close to .
Universal curve showing dependency of the dimensionless wavelength on the electrospinning number : three series of experimental data, distinguished here using various symbols, were obtained using measurements carried out with linear clefts using polyvinyl-alcohol solutions. Circles belong to the distance between the upper edge of the cleft and collector , the distance is assigned to squares and, ultimately, triangles represent the distance . Standard deviations of are in the interval from 0.8 up to 2. The solid, continuous line is plotted according to Eq. (9) for , and solution density , i.e., .
Universal curve showing dependency of dimensionless relaxation time on the electrospinning number .
Linear clefts emit polymeric jets. Clefts in (a) and (b) emit polymeric (polyvinyl alcohol) jets at the voltages, 32 and , respectively. The interjet distance∕wavelength is . The distance between the cleft and the collector was adjusted at .
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